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Abstract:

Input devices configured to provide user interface by detecting three
dimensional movement of an external object are disclosed. The input
device comprises at least two photodetector pairs, a radiation source and
a circuit configurable to detect differential and common mode signals
generated in the photodetector pairs. By detecting the common mode and
differential signals, movement of an external object may be determined
and used to control a pointer, or a cursor.

Claims:

1. An input device configured to provide user interface by detecting
three dimensional movement of an external object, comprising: a
substrate; a radiation source located on the substrate, the radiation
source configured to emit a radiation; a first photodetector pair located
on the substrate with the radiation source located between the first
photodetector pair, wherein the first photodetector pair and the
radiation source are positioned along a first axis, and wherein the first
photodetector pair are configured such that movement of the external
object along the first axis is operable to cause more photo signal to be
generated in one photodetector of the first photodetector pair and less
photo signal to be generated in the other photodetector of the first
photodetector pair; a second photodetector pair located on the substrate
with the radiation source located between the second photodetector pair,
wherein the second photodetector pair and the radiation source are
positioned along a second axis perpendicular to the first axis, and
wherein the second photodetector pair are configured such that movement
of the external object along the second axis is operable to cause more
photo signal to be generated in one photodetector of the second
photodetector pair and less photo signal to be generated in the other
photodetector of the second photodetector pair; and a circuit configured
to detect movement of the external object, wherein movement of the
external object along the first axis is detected through photo signals
generated in the first photodetector pair, movement of the external
object along the second axis is detected through photo signals generated
in the second photodetector pair, and movement along an axis
perpendicular to the first and second axes is detected through photo
signals generated in both the first and second photodetectors pair.

2. The input device of claim 1 further comprising: a third photodetector
pair located on the substrate with the radiation source located between
the third photodetector pair, wherein the third photodetector pair and
the radiation source are positioned along a third axis, and movement of
the external object along the third axis is operable to cause more photo
signal to be generated in one photodetector of the third photodetector
pair and less photo signal to be generated in the other photodetector of
the third photodetector pair; and a fourth photodetector pair located on
the substrate with the radiation source located between the fourth
photodetector pair, wherein the fourth photodetector pair and the
radiation source are positioned along a fourth axis, and movement of the
external object along the fourth axis is operable to cause more photo
signal to be generated in one photodetector of the fourth photodetector
pair and less photo signal to be generated in the other photodetector of
the fourth photodetector pair, wherein the third and fourth axes are
position on the same plane as the first and second axes, and wherein
movement of the external object along the third axis is detected through
photo signals generated in the third photodetector pair, movement of the
external object along the fourth axis is detected through photo signals
generated in the fourth photodetector pair, and movement along an axis
perpendicular to the third and fourth axes is detected through photo
signals generated in both the third and fourth photodetector pairs.

3. The input device of claim 1, further comprising a top plate positioned
above the substrate, wherein the top plate is planarly parallel to the
substrate.

4. The input device of claim 3, further comprising a sensor configured to
produce an output when the external object touches the top plate.

6. The input device of claim 1, wherein the input device further
comprises a reflector dome positioned above the radiation source, the
first and second photodetector pairs, wherein the reflector dome is
configured to reflect the radiation from the radiation source to the
first and second photodetectors pair.

7. The input device of claim 6, wherein the external object compresses
the reflector dome causing more radiation to be reflected onto all, or a
portion of the first or second photodetector pairs.

8. The input device of claim 1, wherein the radiation emitted by the
radiation source has a wavelength between 450 nm to 950 nm.

9. The input device of claim 1, wherein the input device further
comprises an indicating light source configured to provide indication
when the external objected is detected.

10. The input device of claim 1, wherein the input device forms a portion
of a three dimensional navigation device.

11. The input device of claim 1, wherein the input device forms a portion
of a mobile device.

12. A navigation input device configured to provide user interface by
detecting three dimensional movement of an external object, comprising: a
substrate; a radiation source located on the substrate, the radiation
source configured to emit a radiation; a first photodetector pair located
on the substrate with the radiation source located in the middle of the
first photodetector pair, wherein the first photodetector pair and the
radiation source positioned to form a first axis, and movement of the
external object along the first axis is operable to cause more photo
signal to be generated in one photodetector of the first photodetector
pair and less photo signal to be generated in the other photodetector of
the first photodetector pair; a first circuit electrically coupled to the
first photodetector pair, the first circuit configured to produce a first
output signal which correlates to movement of the external object along
the first axis; a second photodetector pair located on the substrate with
the radiation source located in the middle of the second photodetector
pair, wherein the second photodetector pair and the radiation source
positioned to form a second axis perpendicular to the first axis, and
movement of the external object along the second axis operable to cause
more photo signal to be generated in one photodetector of the second
photodetector pair and less photo signal to be generated in the other
photodetector of the second photodetector pair; a second circuit
electrically coupled to the second photodetector pair, the second circuit
configured to produce a second output signal which correlates to movement
of the external object along the second axis; and, a third circuit
electrically coupled to the first and second photodetector pairs, the
third circuit configured to detect movement of the external object along
a third axis perpendicular to the first and second axes, wherein the
third circuit configured to produce a third output signal which
correlates to movement of the external object along the third axis.

13. The navigation input device of claim 12, wherein the navigation input
device further comprises a top plate positioned above the substrate and
wherein the top plate is planarly parallel to the substrate.

14. The navigation input device of claim 13, wherein the navigation input
device further comprises a sensor configured to produce an output when an
external object touches the top plate.

15. The navigation input device of claim 12, wherein the first and second
circuits comprise differential amplifiers.

16. The navigation input device of claim 12, further comprising a
reflector dome positioned above the radiation source and the first and
second photodetector pairs, wherein the reflector dome is configured to
reflect radiation from the radiation source to the first and second
photodetector pairs and wherein the reflector dome is configured to cause
more radiation to be reflected onto all, or a portion of the first or
second photodetector pairs when the reflector dome is compressed by an
external object.

17. The navigation input device of claim 16, wherein the metal dome made
from a resilient material at least partially coated with a metallic or
reflective material.

18. The navigation input device of claim 12, wherein the radiation
emitted by the radiation source has a wavelength between 450 nm to 950
nm.

19. The navigation input device of claim 12, wherein the navigation input
device forms a portion of a mobile device.

20. The navigation input device of claim 12, wherein the input device
forms a portion of a mobile device.

Description:

BACKGROUND

[0001] As most electronic devices and electrical appliances are designed
with liquid crystal display (hereinafter LCD) screens, input devices
capable of controlling a pointer on the screen have become popular. Input
de-vices specifically designed to control a pointer are also known as
navigation input devices. In the past, navigation input devices were
commonly used in computing systems such as desktop computers. Today, many
electronic devices and electrical appliances have an LCD screen that
utilizes a navigation input device.

[0002] Utilizing a navigation input device, a user may navigate a pointer
on a screen over a graphical user interface. Examples of navigation input
devices typically used today include a mouse, a touch screen, and a touch
pad. Most navigation input devices are operable to control a pointer in a
two dimensional plane, although the graphical user inter-face may be
three dimensional (referred hereinafter as 3D) in a virtual space.
Navigation input devices capable of controlling a pointer in a virtual 3D
space are known as a three dimensional navigation devices.

[0003] Some navigation input devices with small form factors may be
operated using a finger, such as a touch screen or touch pad. These
navigation input devices are becoming popular in portable devices, such
as mobile phones, portable game consoles, portable electronic readers,
and similar devices.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Illustrative embodiments by way of examples, not by way of
limitation, are illustrated in the drawings. Throughout the description
and drawings, similar reference numbers may be used to identify similar
elements.

[0012]FIG. 8 shows a flow chart illustrating a method for making input
de-vice.

DETAILED DESCRIPTION

[0013]FIG. 1 illustrates an embodiment showing isometric view of an input
device 100 which may comprise photodetector pairs 211-214, a radiation
source 220 and a substrate 210. The radiation source 220 and the
photodetector pairs 211-214 may be attached to the substrate 210 such
that the radiation source 220 and a first photodetector pair 211-212 may
be positioned along a first axis 101. The radiation source 220 and a
second photodetector pair 213-214 may be positioned along a second axis
102 perpendicular to the first axis 101. The first and second axes
101-102 may be positioned planarly parallel to the substrate 210. The
input device 100 may be configured to detect movement of an external
object along the first axis 101, the second axis 102 or an axis 103
perpendicular to the first and second axes.

[0014] The radiation source 220 may be a light source emitting visible
light, or a radiation source emitting radiation invisible to human eye
such as infrared or ultraviolet (UV) radiation. The choice of utilizing a
visible or an invisible light source depends on the design requirements.
A visible light source, such as any color light emitting diode (referred
to hereinafter as LED) may be appealing in terms of look but some users
may prefer to work on a device without visible light. In such situations,
an LED emitting UV or infrared radiation may be employed. For consumer
products, infrared radiation sources may be commonly used.

[0015] The photodetector pairs 211-214 may be photodiodes,
phototransistors or photodiodes with integrated amplifiers. For example,
using a conventional CMOS process, the photodetectors 211-214 may be
photodiodes implemented using a N-type well and P-type substrate.
Depending on the process, the photodiode may have a peak spectral
response at a wavelength between 450 nm-950 nm. Correspondingly, the
radiation source 220 may be configured to emit radiation with a
wavelength between 450 nm-950 nm to obtain optimal performance.

[0016] FIGS. 2A-2B illustrate how the input device 100 may be operable to
detect movement of an external object 120, such as a finger, a reflector
held by a hand, or something similar. For simplicity of illustration,
only the first photodetector pair 211-212 and the radiation source 220
are illustrated. With reference to FIG. 2A, the radiation source 220 may
be positioned between the first photodetector pair 211-212. When the
external object 120 is not positioned within the range of a predetermined
distance, radiation emitted by the radiation source 220 may not be
reflected at all. Even if the radiation is being reflected, the radiation
may be substantially low, or may not fall on the photodetectors 211-212.
The predetermined distance may be in a range of a few centimeters or tens
of centimeters from the photodetectors 211-212 when measured along the
axis 103.

[0017] With reference to FIG. 2A, when an external object 120 is within
the range of the predetermined distance, the radiation emitted by the
radiation source 220 may be reflected and received by both the
photodetectors 211-212. Movement of the external object 120 along the
first axis 101 may be configured to cause a larger signal to be generated
in one photodetector of the first photodetector pair 211-212 and less
signal to be generated in the other photodetector of the first
photodetector pair 211-212.

[0018] For example, when the external object 120 is positioned above the
photodiode, radiation from the radiation source 220, such as ray 130, may
be reflected equally to the photodetectors 211-212 such that signals
generated at both photodetectors 211-212 may be substantially equal.
However, when the external object 120 moves along the first axis 101
towards photodetector 212, radiation from the radiation source 220, as
shown by ray 131, may be reflected more towards photodetector 212. As a
result, a larger signal may be generated in the photodetector 212 than
the photodetector 211. This may create a differential signal between the
photodetector pair 211-212, which correlates to movement along the first
axis 101 in the direction of photodetector 212 and away from
photodetector 211.

[0019] Similarly, movement of the external object 120 along the second
axis 102 (shown in FIG. 1) may be determined using the second
photodetector pairs 213-214 (shown in FIG. 1) following the same method.
Consequently, by monitoring the differential signal values generated by
the both photodetector pairs 211-2 and 213-214, the position of the
external object 120 along the plane planarly parallel to the substrate
210 may be determined.

[0020] With reference to FIG. 2B, when the external object 120 moves along
the axis 103 perpendicular to the first and second axes 101-102,
radiation emitted by the radiation source 220 which is reflected to both
the photodetectors 211-212 may be reduced equally. Correspondingly, when
the external object 120 moves further away beyond the predetermined
distance, then the reflected radiation becomes undetectable.

[0021] In the embodiment shown in FIG. 2B, when the external object 120 is
positioned above and substantially in the middle of the photodetectors
211-212, radiation emitted by the radiation source 220, as shown by ray
140, may be reflected substantially proportionately to both
photodetectors 211-212. Even when the external object 120 moves further
away along the axis 103, radiation emitted by the radiation source 220,
as shown by ray 141, may still be reflected proportionately to both
photodetectors 211-212. However, when the external object 120 moves
further away, the radiation received by the photodetectors 211-212 may be
reduced proportionately in each of the photodetectors 211-212. The same
phenomenon may also be observed at the second photodetector pair 213-214.

[0022] As explained above, the movement of the external object 120
substantially along the axis 103 perpendicular to the first and second
axes 101-102 may be determined by proportionate signals being generated
in all the photodetectors 211-214. Movement of the external object 120
along the axis 103 may also be determined by detecting common mode of the
signals generated in the first and second photodetector pairs 211-214.
Common mode signals may be signals when a differential pair signals move
in same direction and will be explained in next paragraphs.

[0023]FIG. 3 illustrates an embodiment of a circuit 300 electrically
coupled to the first and second photodetector pairs 211-214. The circuit
300 may comprise differential amplifiers 251-252. The differential
amplifier 251 may be electrically coupled to the first photodetector pair
211-212. For example, when a radiation is being reflected onto the first
photodetector pair 211-212, photocurrents I11 and I12 may be
generated in the photodetectors 211-212, respectively. Similarly, the
second photodetector pair 213-214 may be operable to generate
photocurrents I21 and I22, respectively when radiation is
reflected onto the second photodetector pair 213-214.

[0024] The output from the photodetectors 211-214 may be electrically
coupled to the differential amplifiers 251-252. In other words, the
output from the photodetectors 211-214 may be directly connected to the
differential amplifiers 251-252 or may be connected to the differential
amplifiers 251-252 indirectly through current buffers, capacitors or some
other electrical components (not shown). The differential amplifiers
251-252 may be conventional fully differential amplifiers with feedback.
The detailed construction of the differential amplifiers 251-252 may be
done by a person with ordinary skills in the art.

[0025] The differential amplifiers 251-252 may be configured to produce
voltage outputs V1 and V2, respectively. The voltage output
V1 may be proportional to the differential value of photocurrents
I11 and I12, and the voltage output V2 may be proportional
to the differential value of photocurrents I21 and I22,
respectively.

[0026] For example, referring to FIG. 2A and FIG. 3, when more radiation
is being reflected onto the photodetector 212 compared to photodetector
211, as illustrated in FIG. 2B, I12 may increase and I11 may
decrease. As a result, the differential signal generated by I11 and
I12 may increase, and this may yield a larger voltage output of
V1. When an equal amount of the radiation is being reflected onto
the photodetectors 211-212, the photo current generated I21 and
I22 may have a substantially similar value, thus resulting in a
smaller differential value, and thus, yield a small voltage output of
V1 from differential amplifier 251. When the external object 120
moves in the opposite direction towards photodetector 211, the voltage
output of V1 may decrease further or may become a negative value.

[0027] In short, the voltage output of V1 may be configured to
indicate movement along the first axis 101 (as shown in FIG. 1). In a
similar way, the voltage output of V2 may be configured to indicate
movement along the second axis 102 (as shown in FIG. 1) using the second
photodetector pair 213-214 and the differential amplifier 252.

[0028] Usually, a differential amplifier, which is configured to produce a
differential output signal, can also be configured to produce an output
proportional to the common mode signal with little modification. In the
embodiment shown in FIG. 3, the common mode of the photocurrents I11
and I12, and photocurrents I21 and I22 may be detected
using the differential amplifiers 251-252 and amplified as Vc1 and
Vc2, respectively.

[0029] For example, referring to FIG. 2B and FIG. 3, when the external
object 120 moves along the axis 103 further away from the radiation
source 220, the absolute value of I11 and I12 may decrease
simultaneously, and thus, cause the common mode signal Vc1 to
decrease accordingly. However, note that the voltage output V1 may
remain unchanged because the photodetector pair 211-212 may be receiving
the same amount of radiation.

[0030] In the opposite scenario, when the external object 120 in FIG. 2A
moves toward the radiation source 220, both I11 and I12
increase simultaneously, causing the common mode signal Vc1 to
increase accordingly. The common mode signal Vc2 generated using the
second photodetector pair 213-214 may behave in a similar manner.
Movement along the axis 103 perpendicular to the first and second axes
101-102 may be determined by using the common mode signal Vc1 of the
first photodetector pair 211-212, or by using the common mode signal
Vc2 of the second photodetector pair 213-214, or by using both
common mode signals Vc1 and Vc2. For example, in the circuit
300 shown in FIG. 3, a "select the stronger" method may be used.

[0031] Referring to FIG. 3, the common mode signals Vc1 and Vc2
may be connected to a comparator 253. In the embodiment shown in FIG. 3,
the comparator 253 may be indirectly connected to the output of
photodetector pairs 211-214. The output of the photodetector pairs
211-214 may be first connected to the differential amplifiers 251-252, in
which the output may be then connected to the comparator 253.

[0032] For example, when the common mode signal generated in the first
photodetector pair 211-212 Vc1 becomes higher than the common mode
signal generated in the second photodetector pair Vc2, the output of
the comparator 253 may become logic Low, and thus turns off switch S1.
The output of the comparator 253 may be connected to an inverter 254
which turns on the switch S2. As a result, the common mode signal
Vc1 may be selected as the voltage output V3 indicating the
movement along the axis 103.

[0033] On the other hand, when the common mode signal Vc1 becomes
lower than the common mode signal Vc2, the output of the comparator
253 may turn logic High, and thus turns on switch S1. The inverter 254
may be operable to turn off the switch S2. Thus, the common mode signal
Vc2 may be selected as the voltage output V3. Other methods may
be used, such as multiplying the common mode signals Vc1 and
Vc2 with a weighting factor, or alternatively, taking average values
can also be used with additional logic or digital processing circuits. In
some situations, further digital signal processing may be performed. In
such circumstances, an analog to digital converter may be'connected to
the voltage outputs V1, V2, Vc1 and Vc2 to convert
the analog values into digital values for digital signal processing.

[0034] The input device 100 may be used in three dimensional navigation
applications. Most of the 3D games today are played using conventional
mice, which are two dimensional navigation devices. Although a two
dimensional navigation device may be used for 3D game applications,
having a three dimensional navigation device may add realness or vivid
feel to the games. This can be understood because a two dimensional
navigation device may not be able to produce an input for a virtual 3D
space. For example, consider playing a 3-D ping pong game using a
conventional mouse to hold a ping pong "bat". The two dimensional device
can only allow the user to move the "bat" by pointing at the two
dimension screen. However, using a 3-D navigation device permits the user
to control the "bat" moving forward, backward, up, clown, left or right,
reflecting precisely what happens in reality.

[0035] For conventional two dimension navigation applications, the
movement along the axis 103 may be used for additional functions, such as
replacing "right click" or "left click" found in existing navigation
applications. In addition to navigation applications, the input device
100 may be used as a directional input device, such as a joystick, or
replacing a job dial wheel found in some mobile phone devices, or
replacing multiple input keys found in some key pads.

[0036] The input device 100 shown in FIG. 1 may be supplemented with
additional elements such as additional sensors and indicator light
sources to provide more functionality. For example, FIG. 4 illustrates an
alternate embodiment showing isometric view of an input device 400 which
may comprise photodetector pairs 211-214, a radiation source 220, a
substrate 210, a top plate 260, a sensor 270, and an indicator light
source 280.

[0037] The top plate 260 may be positioned planarly parallel and above the
substrate 210. The top plate 260 may be made from plastic, glass, poly
urethane, or other similar materials. The top plate 260 may be configured
to prevent dust from gathering at the radiation source 220 or the
photodetectors 211-214. The top plate 260 may or may not be transparent
to the human eye but may be made transparent to the radiation emitted by
the radiation source 220.

[0038] The sensor 270 may be configured to produce an output when the
external object touches the top plate 260. For example, in FIG. 4, the
sensor 270 may be a vibration sensor or a capacitive sensor configured to
produce an output when an external object such as a finger taps on the
top plate 260. The sensor 270 may be positioned on the substrate 210, or
on the top plate 260.

[0039] The sensor 270 may be configured to be used as additional input
terminals. For example, when the navigation device 400 is used as a three
dimensional navigation device controlling the position of a virtual
pointer in a 3D game, a tap on the top plate 260 may be configured to be
an input to reset the position of the virtual pointer to a default
position. Additional sensors similar to the sensor 270 may be added to
the input device 400.

[0040] In order to make the input device 400 more user friendly,
additional user interface such as indicator light source 280 may be
added. For example, the indicator light source 280 may be configured to
be turned on when an external object is detected. This feature may be
useful if the radiation emitted by the radiation source 220 is not
visible to the human eye. For designs with visible radiation source 220,
a similar user interface may be achieved by powering up more radiation
when an external object is detected.

[0041] The input devices shown in FIG. 1 and FIG. 4 have two pairs of
photodetectors 211-214. However, more photodetectors pairs may be added.
For example, FIG. 5 illustrates a top view of an input device 500 with
four pairs of photodetectors. The input device 500 comprises a substrate
210, a radiation source 220, first and second photodetector pairs 211-214
as found in the input device 100. The input device 500 also comprises a
third photodetector pair 215-216 and a fourth photodetector pair 217-218.

[0042] The third photodetector pair 215-216 may be positioned along a
third axis 105 whereas the fourth photodetector pair 217-218 may be
positioned along a fourth axis 106. Similar to the arrangement in the
first and second photodetector pairs 211-214, the radiation source 220
may be positioned in the middle of the respective third and fourth
photodetector pairs 215-218. The first and second axes 101-102, as well
as the third and fourth axes 105-106 may be positioned in a plane
planarly parallel to the substrate 210. The third axis 105 may be
substantially perpendicular to the fourth axis 106. The third axis 105
and the first axis 101 may be at a predetermined angle, for example, 45
degrees. Similarly, the fourth axis 106 and the second axis 102 may be at
a predetermined angle, such as 45 degrees.

[0043] The third and fourth photodetector pairs 215-216 may be operable to
detect movements of an external object along the third and fourth axes in
a similar manner to the discussion of the first and second photodetector
pairs 211-214 in FIG. 2A. Similarly, the third and fourth photodetector
pairs 215-216 may be operable to detect movement of an external object
along an axis 103 perpendicular to the substrate 210 in a similar manner
shown in FIG. 2B. The third and fourth photodetector pairs 215-216 may be
connected to a circuit as discussed earlier with respect to FIG. 3.

[0044] Movements along the third and fourth axes 105-106 may be converted
to the first and second axes 101-102 using multiplying factors. For
example, if the third axis forms a degree of 45 degree with the first and
second axes, the detected readings can be converted to the first and
second axes by multiplying the reading with cosine 45 and sine 45
respectively. The detection from the third and fourth photodetector pairs
215-218 may be used to supplement the detection of the first and second
photodetector pairs 211-214 in order to achieve further precision.

[0045] The input device 100 shown in FIG. 1 may be made more energy
efficient and reliable by utilizing a reflector dome rather than relying
on the reflection by an external object 120. Usually, a reflector can
reflect more radiation than an external object 120 which may not be
reflective. FIG. 6 illustrates an embodiment showing isometric view of an
input device 600 with a reflector dome 230. The input device 600 may
comprise a substrate 210, first and second photodetector pairs 211-214, a
radiation source 220, and a reflector dome 230.

[0046] The reflector dome 230 may be positioned above the radiation source
220 such that radiation emitted from the radiation source 220 may be
reflected substantially proportionately to all the photodetectors
211-214. The reflector dome 230 may be made from an elastic, reflective
material. For example, the reflector dome 230 may be a thin metal dome or
a rubber type material with interior surface coated with reflective
material. It should be noted that although FIG. 6 illustrates two
photodetector pairs 211-214, this is equally applicable to four
photodetector pairs as shown in FIG. 5 or more photodetector pairs.

[0047] FIGS. 7A-7C illustrate how the input device 600 detects movement
using a cross-sectional view of the input device 600 along line 3-3 shown
in FIG. 6. As shown in FIG. 7A, without the presence of any external
object 120, radiation from the radiation source 220, as shown by ray 150,
may be reflected substantially proportionately to the photodetector pair
211-212.

[0048] Without the presence or compression from external object 120, the
input device 600 may be in an idle mode. However, when an external object
120 first compresses the reflector dome 230 to a default position as
shown in FIG. 7c, the input device 600 may be configured to be in an
operation mode and starts to detect movements.

[0049] FIG. 7B illustrates how movement along the first axis 101 may be
detected. When an external object 120, such as a human finger, compresses
the reflector dome 230 in a certain direction as shown in FIG. 7B, the
reflector dome 230 may be deformed such that more radiation, as shown by
ray 151, may be directed more toward one photodetector 212 compared to
another photodetector 211 of the first photodetector pair 211-212. The
mechanism of how the input device 600 works may be similar to the input
device 100 discussed in FIG. 2B except that more radiation may be
reflected, as the flexible, reflective dome may reflect more light than
an external object 120, such as a finger. The reflective dome may be made
from a flexible metallic material, or any resilient material that is
either reflective or at least partially coated by a metallic or
reflective material.

[0050] When the reflector dome 230 is being compressed evenly by the
external object 120 as shown in FIG. 7c, the photodetector pair 211-212
may receive substantially similar amount of reflection but as the
reflector dome 230 is being moved closer to the photodetectors 211-212,
the common mode signal generated by the photodetectors 211-212 may
increase. Similar to discussion in FIG. 2B and FIG. 3, movement of the
external object 120 in the axis perpendicular to the substrate may be
detected in this situation.

[0051]FIG. 8 shows a flow chart 700 illustrating a method for making the
input device 100 shown in FIG. 2. In step 810, a first photodetector pair
and a radiation source may be positioned on a substrate along a first
axis. The radiation source may be positioned in the center of the first
photodetector pair such that movement of an external object along the
first axis operable to cause more photo signal generated in one
photodetector of the first photodetector pair and less photo signal to be
generated in the other photodetector of the first photodetector pair.

[0052] The method 800 then proceeds to step 820, in which a second
photodetector pair and the radiation source may be positioned on the
substrate along a second axis perpendicular to the first axis. The first
and second axes may be planarly parallel to the substrate. The radiation
source may be positioned in the center of the second photodetector pair.
Similar to step 810, movement of the external object along the second
axis may be operable to cause more photo signal generated in one
photodetector of the second photodetector pair and less photo signal to
be generated in the other photodetector of the second photodetector pair.

[0053] The method 800 then proceeds to step 830, in which the first and
second photodetector pairs may be electrically coupled to a circuit. The
circuit may be configured to detect movement of the external object such
that movement of the external object along the first and second axes are
detected through differential photo signals generated in the first and
second photodetector pairs respectively. Movement along an axis
perpendicular to the first and second axes detected through the common
mode photo signals generated in the first and second photodetector pairs.
For additional features, for example top plate as shown in FIG. 4,
additional steps of positioning a top plate planarly parallel to the
substrate above the radiation source, the first and second photodetector
pairs may be needed. Similarly, if a flexible, reflective dome is
utilized, additional processing steps may be necessary.

[0054] Although specific embodiments of the invention have been described
and illustrated herein above, the invention is not to be limited to the
specific forms or arrangements of parts so described and illustrated. For
example, radiation source described above may be LEDs as disclosed in the
embodiments herein, but can also be a laser, or some other future light
source. The scope of the invention is to be defined by the claims
appended hereto and their equivalents.